We came close to splitting up over it and I had to pack her bag for her and ask her to leave. I have told husband how much of a threat to our marriage this is. He stands firm that it suits him to have her there... i am livid!!!
Have you reminded him of this time ?
To the posters complaining about "MiL hate" on MN, this isn't about the way the OP is related to her, it is everything to do with the personality of the person, not that she happens to be DM's mother. It is about the interfering and not respecting boundaries.
I don't hate my MiL either, but we have different ways of living our lives, and there is no way in a million years we could live next door to each other. My mother - I wouldn't have had such an issue with, as she would have respected boundaries, but it does rather put all the onus on you for care as they get older, rather than a joint responsibility with siblings. that isn't just because it is my mother... my dh would say the same. He'd far sooner share a boundary with my folks than his - it is personality not relationship.
However, moving would cost your MiL a fortune (selling costs, moving costs, buying costs, plus all the disruption of moving, plus how she manages the renovations, plus extra expense of then getting new curtains etc and potentially furniture that fits). If it is time to move, then you suck that up, but if she is in the next street anyway, then all the 'looking after dc / dc popping round on their own / dh popping in for 30mins' type stuff can still go on without her moving, I'd have thought?